Methods of this kind are known, for example from the article by L. S. Davis "A Survey of Edge Detection Techniques" in "Computer Graphics and Image Processing" 1975, No. 4, pp. 248-270. Such methods use various linear or non-linear operators which offer various advantages and involve a different arithmetical complexity. Notably when real images which are degraded by noise and interference signals are used, the various methods offer different results. Such images may be, for example X-ray images or images obtained by magnetic resonance imaging. In practical images a problem occurs in that edges cannot be defined exactly to one point or a more or less strict sequence of individual pixels, and on the other hand the known methods often cause gaps in the detected edges, i.e. non-contiguous contours.